(67b) Unravelling the Detailed Characterization of Hydroprocessing Feeds and Products

Clean fuel legislation in Europe, America and Asia is driving the demand for ultra-low sulfur diesel (ULSD) fuel, requiring a total sulfur content around 10 ppm after 2008. Further improvement in diesel hydrotreatment (HDT) will depend on the accurate understanding of the phenomena involved at the molecular scale. Therefore, it is of major importance for refiners to get an accurate characterization of HDT feeds and products, for both hydrocarbons, sulfur and nitrogen species. Due to the complexity of diesel cuts, conventional gas phase chromatography is unable to provide a detailed description of diesel samples.

The recent development of comprehensive two-dimensional gas phase chromatography (GC*GC) over the last years has been a turning point in the molecular characterization of gas-oils. The presentation will describe the advances obtained by IFP in the characterization of hydrocarbons, sulfur and nitrogen compounds.

GC*GC hyphenated with a flame ionisation detector allows a detailed quantification of hydrocarbons both by families and by numbers of carbon atoms. This technique can especially be applied to the quantification of mono, di and tri-aromatics, as well as mono, di and tri-naphtenes.

The use of specific detectors based on chemiluminescence enables to separate and quantify sulfur and nitrogen species. Through the sulfur speciation method, alkylated benzothiophenes and dibenzothiophenes from diesel feeds are separated and quantified by numbers of carbon atoms. On the other way, the nitrogen speciation method developed in IFP allows an unambiguous separation of basic and non basic compounds into well defined families (pyridines, anilines, quinolines, acridines, indoles, carbazoles). Both speciation techniques have recently been applied to diesel HDT products, allowing the identification and quantification of the most refractory compounds towards hydrodesulfurization and hydrodenitrogenation.

Therefore, GC*GC offers an interesting perspective in the monitoring of reactions involved in hydrotreatment processes.